Carbon nanotubes (CNTs) are promising and useful materials for
several applications due to their good thermal, electrical,
optical and mechanical properties. Many studies have been
performed in the past decade to explore and develop devices
which could leverage the excellent properties of individual CNTs
and their two- and three-dimensional (2D and 3D) networks. In
particular, CNT network thin film transistors (CN-TFTs) have
been explored for a wide range of applications such as flexible
displays, sensors, antennas, etc. CNT networks are typically
supported on thermally insulating substrates such as glass or
plastics, which have very low thermal conductivity and where the
excessive self-heating in CN-TFTs under high field operations
can lead to the breakdown of these devices. In addition, the
variations in the channel geometry and network morphology are
very likely to influence the reliability and breakdown behavior
of CN-TFTs as well. The variation in the breakdown behavior for
a given TFT geometry can lead to instability and/or
unreliability during the operation of CN-TFTs. Thus, it is very
important to understand how the geometrical parameters affect
the high-field operation of the CN-TFT in order to optimize the
device design for reliable and uniform behavior. We apply both
experimental and computational methods to understand the
breakdown behavior and thermal reliability of CN-TFTs. We
examine the breakdown characteristics, such as peak power and
the breakdown voltage of CN-TFTs, to find their relation with
the aforementioned geometrical parameters. The analysis on
breakdown behavior of CN-TFTs can provide useful insights and
design guidelines for highly reliable, uniform and improved
thermal/electrical performance of these devices.

(a) Comparison of
random CNT network from simulations (left inset, channel region)
with scanning electron microscopy (SEM) image of the CN-TFT used
in experiments after the breakdown, respectively. The red dotted
line shows the breakdown pattern of the network. (b) Comparison
of computational results to experimental measurements of
dissipated power vs. source-drain voltage; the dark blue curve
shows the statistical average of 50 random networks (dashed
curves) obtained from the simulations.

Temperature profile in CNT networks for different values
of thermal contact conductances at CNT junction (BiC)
and CNT-substrate interface (BiS) at different
source to drain voltage (VSD) (a) 3 V, (b)
8 V, (c) 13 V, (d) 27 V. Network density = 3.5
CNTs/µm2. In each case the current flows from left to right
(source to drain) of the panels, respectively. High voltage
leads to excessive heat dissipation leading to breakdown of
the CNT network.